On 10/09/2023 19:46, Qais Yousef wrote:
> On 09/08/23 16:30, Vincent Guittot wrote:
>
[...]
>>>> above 512 whatever the current (720) formula or your proposal (608).
>>>> In the case of uclamp, it should be applied after having been scaled
>>>> by irq time.
>>>
>>> I lost you a bit here. I'm not sure how you reached the 720 and 608 numbers.
>>
>> My bad, I finally decided to use an irq pressure of 128 in my
>> calculation but forgot to change the value in my email
>>
>>>
>>> So the way I'm proposing it here
>>>
>>> util = cfs + rt + dvfs_headroom(cfs+rt) = 800 + 0.25 * 800 = 1000
>>> util = uclamp_rq_util_with(rq, util, NULL) = 512
>>> util = scale_rq_capacity(512, 256, 1024) = 0.75 * 512 = 384
>>> util += dvfs_headroom(irq) = 384 + 256 + 0.25 * 256 = 704
>>> util += dvfs_headroom(dl_bw) = 704
>>>
>>>>
>>>> So we should have reported utilization of 720 with a bandwidth
>>>> requirement of 512 and then cpufreq can applies its headroom if needed
>>>
>>> The key part I'm changing is this
>>>
>>> util = cfs + rt + dvfs_headroom(cfs+rt) = 800 + 0.25 * 800 = 1000
>>> util = uclamp_rq_util_with(rq, util, NULL) = 512
>>>
>>> Before we had (assume irq, rt and dl are 0 for simplicity and a single task is
>>> running)
>>>
>>> util = cfs = 800
>>> util = uclamp_rq_util_with(rq, util, NULL) = 512
>>> util = dvfs_headroom(util) = 512 * 0.25 * 512 = 640
>>>
>>> So we are running higher than we are allowed to. So applying the headroom
>>> after taking uclamp constraints into account is the problem.
I'm not sure I understood all the example math in this thread correctly:
Examples:
irq = 128 or 256
util = 800 uclamp = 512
--- current code:
((util_cfs + util_rt) * ((max - irq) / max) + irq + dl_bw) * scale
<- uclamped(cfs+rt) ->
<-- scale_irq_capacity() -->|<-- map_util_perf()
/ (headroom())
irq = 128: (512 * (1024 - 128) / 1024 + 128 + 0) * 1.25 = 576 * 1.25 = 720
irq = 256: (512 * (1024 - 256) / 1024 + 256 + 0) * 1.25 = 640 * 1.25 = 800
--- new approach:
irq = 128: (512 * (1024 - 128) / 1024 + 128 + 0.25 * 128) = 608
irq = 256: (512 * (1024 - 256) / 1024 + 256 + 0.25 * 256) = 704
<->
uclamped(cfs+rt+headroom(cfs+rt))
<- scale_irq_capacity() ->
<-- headroom(irq) ? -->
Is the correct?
[...]
On 09/12/23 15:40, Dietmar Eggemann wrote:
> On 10/09/2023 19:46, Qais Yousef wrote:
> > On 09/08/23 16:30, Vincent Guittot wrote:
> >
>
> [...]
>
> >>>> above 512 whatever the current (720) formula or your proposal (608).
> >>>> In the case of uclamp, it should be applied after having been scaled
> >>>> by irq time.
> >>>
> >>> I lost you a bit here. I'm not sure how you reached the 720 and 608 numbers.
> >>
> >> My bad, I finally decided to use an irq pressure of 128 in my
> >> calculation but forgot to change the value in my email
> >>
> >>>
> >>> So the way I'm proposing it here
> >>>
> >>> util = cfs + rt + dvfs_headroom(cfs+rt) = 800 + 0.25 * 800 = 1000
> >>> util = uclamp_rq_util_with(rq, util, NULL) = 512
> >>> util = scale_rq_capacity(512, 256, 1024) = 0.75 * 512 = 384
> >>> util += dvfs_headroom(irq) = 384 + 256 + 0.25 * 256 = 704
> >>> util += dvfs_headroom(dl_bw) = 704
> >>>
> >>>>
> >>>> So we should have reported utilization of 720 with a bandwidth
> >>>> requirement of 512 and then cpufreq can applies its headroom if needed
> >>>
> >>> The key part I'm changing is this
> >>>
> >>> util = cfs + rt + dvfs_headroom(cfs+rt) = 800 + 0.25 * 800 = 1000
> >>> util = uclamp_rq_util_with(rq, util, NULL) = 512
> >>>
> >>> Before we had (assume irq, rt and dl are 0 for simplicity and a single task is
> >>> running)
> >>>
> >>> util = cfs = 800
> >>> util = uclamp_rq_util_with(rq, util, NULL) = 512
> >>> util = dvfs_headroom(util) = 512 * 0.25 * 512 = 640
> >>>
> >>> So we are running higher than we are allowed to. So applying the headroom
> >>> after taking uclamp constraints into account is the problem.
>
> I'm not sure I understood all the example math in this thread correctly:
>
> Examples:
>
> irq = 128 or 256
>
> util = 800 uclamp = 512
>
>
> --- current code:
>
> ((util_cfs + util_rt) * ((max - irq) / max) + irq + dl_bw) * scale
>
> <- uclamped(cfs+rt) ->
>
> <-- scale_irq_capacity() -->|<-- map_util_perf()
> / (headroom())
>
> irq = 128: (512 * (1024 - 128) / 1024 + 128 + 0) * 1.25 = 576 * 1.25 = 720
>
> irq = 256: (512 * (1024 - 256) / 1024 + 256 + 0) * 1.25 = 640 * 1.25 = 800
>
>
> --- new approach:
>
> irq = 128: (512 * (1024 - 128) / 1024 + 128 + 0.25 * 128) = 608
>
> irq = 256: (512 * (1024 - 256) / 1024 + 256 + 0.25 * 256) = 704
>
> <->
> uclamped(cfs+rt+headroom(cfs+rt))
>
> <- scale_irq_capacity() ->
>
> <-- headroom(irq) ? -->
>
>
> Is the correct?
Yes, this is my understanding too. But I'm not sure anymore as it seems I'm
missing something from what Vincent is saying.
Thanks!
--
Qais Yousef